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AMC0311S: Functional Mode "Missing High Side Supply"

Renan Santos Adriano
Mastermind 25135 points

Part Number: AMC0311S

Hello Experts,

I have a question regarding AMC0311S. The datasheet states in Table 7.1, 'Device Operational Modes,' that if the high-side supply is missing, the OUT pin should be driven to the VREF level. In my application, this is not working.

If the high-side supply fails and there is a 0.4V offset voltage at the VREF pin, the voltage at the OUT pin is only approximately 60 mV. Low Side supply is stable at 5.1V, Power supply pins are buffered with 100n and 1µ as recommended in datasheet. The circuitry is the same as your Typical Application example in the datasheet, except of REFIN Pin is driven to 0.4V.

During normal operation (with the high-side supply present), the 0.4V offset is applied correctly. 

Are there any known topics regarding this behaviour? 

Best regards!

Moritz Nüßlein

  • 0
    TI__Guru 56942 points

    Hi Moritz, 

    Let me please look into this for you. 

  • 0
    TI__Expert 4121 points

    Hello Moritz, I apologize it took us longer to reply. I will support you with this issue. 

    Could you please share a piece of the circuit diagram, or at least tell us how exactly you generate the REFIN voltage?

    There are various methods using e.g. a voltage divider. However, the REFIN input has certain input resistance (impedance). Is the 0.4V measured directly at the pin?

    Meanwhile, I am going to find a PCB and test the issue in application.

    Best regards, Jiri Panacek, Systems Applications Engineer

  • 0 in reply to Jiri Panacek85
    Prodigy 10 points

    Hello Jiri,

    Thank you for your response. I measured the applied offset voltage directly at the IC pin and found it to be 0.4V. This voltage is generated by a reference diode, which is then divided down to 0.4V using a voltage divider (in range of a few kOhms). I am aware of the input resistance of approximately 90 kOhm and have taken it into account in my calculations.

    Thank you for your investigation.

  • 0 in reply to Moritz Nüßlein
    TI__Expert 4121 points

    Hello Mortiz, 

    I will reach out to you over the email. 
    Kind regards, Jiri Panacek